Seattle Public Utilities

About the Utility

Seattle Public Utilities (SPU) runs three City of Seattle utilities: water, drainage and wastewater, and solid waste. The water system and the drainage and wastewater system are financed separately, each through City revenue bonds secured by its own net revenue and rated Aaa and AA+ for water, Aa1 and AA+ for drainage and wastewater. The Water System serves retail customers in Seattle and part of unincorporated King County, and sells wholesale to 17 suburban water districts and municipalities plus the Cascade Water Alliance. In 2025 it served an estimated 1,687,000 people. For wastewater, SPU operates the collection and drainage networks, while treatment is charged through separate County treatment rates.

Water System

Supply comes from two mountain watersheds east of the city, the Cedar River and the South Fork Tolt, and is treated at the Cedar and Tolt treatment facilities under long-term contracts with Jacobs and American Water/CDM. Firm yield is 172 MGD, and the official demand forecast stays considerably below it until well into the future. Under the Muckleshoot Indian Tribe settlement, the City also dedicated water rights above 124 MGD to instream flows. Distribution System Leakage was 4.5% in 2025, with a three-year average of 5.2% against a 10% compliance threshold.

Wastewater System

SPU's wastewater role is collection and drainage: it owns and operates the city's sewers, storm drains, drainage ditches and pump stations, while treatment is charged through separate County treatment rates. Its system has 82 permitted CSO outfalls, regulated under an NPDES permit and a federal Consent Decree entered in 2013 and modified in May 2025. In 2025, the four outfalls to be controlled by the Ship Canal Water Quality Project produced 98 of the 162 CSOs from SPU outfalls. Sanitary sewer overflows remain within their target on a two-year moving average.

Investment & Priorities

Each system has its own adopted six-year capital programme. The 2025–2030 water programme prioritised seismic upgrades of reservoirs and tanks, reservoir covering and storage replacement, and renewal of mains, valves, meters and pump stations. The largest wastewater commitment is the Ship Canal Water Quality Project, a storage tunnel built jointly with King County to control combined sewer overflows. Its main tunnel was completed in 2023 and construction is expected to finish in 2027; the estimated cost has moved from $570 million in 2021 disclosures to approximately $710 million.

Sustainability & Resilience

For supply, SPU's water system plan found that significant investment in new sources would not be needed to address potential climate impacts until approximately 2060. A climate vulnerability assessment covered floods, drought and wildfire, and a Forest Management Plan for the Cedar River Watershed targets wildfire risk. Watershed stewardship sits under a 50-year Habitat Conservation Plan agreed with state and federal governments. Saving Water Partnership members stay below a 110 mgd retail-use goal, and SPU aims for carbon-neutral operations by 2030.

Key Challenges

1. Completing the Ship Canal Water Quality Project, whose four outfalls produced 98 of 162 combined sewer overflows in 2025.
2. Delivering seismic upgrades to water reservoirs and tanks.
3. Financing two large capital programmes while SPU bills, which have outpaced inflation and income growth since 2010, keep rising.
4. Protecting the Cedar River and South Fork Tolt watersheds from wildfire, drought and flood risk.

Major Projects